Transmission apparatus and transmission method

ABSTRACT

A transmitter transmits data to a communicating opponent with a better channel condition with use of one or more frequency blocks including one or more carrier frequencies. The transmitter includes a communicating opponent selection unit evaluating the channel condition for each frequency block for each of plural communicating opponents and selecting one or more communicating opponents from the plurality of communicating opponents, a modulation scheme determination unit determining at least a modulation scheme depending on the evaluated channel condition, a control channel generation unit generating a control channel indicative of the determined modulation scheme and one or more frequency blocks available for the selected communicating opponents to receive a data channel, and a channel transmission unit providing the selected communicating opponents with the control channel and the data channel modulated in accordance with the modulation scheme.

TECHNICAL FIELD

The present invention relates to the technical field of radiocommunication. More specifically, the present invention relates to atransmission apparatus and a transmission method for use in acommunication system for scheduling packets on a downlink.

BACKGROUND ART

In the third generation communication scheme, typically IMT-2000(International Mobile Telecommunications-2000), the informationtransmission rate higher than 2 Mbps is implemented with use of 5 MHzfrequency band in the downlink. In the IMT-2000, the single-carrier typeW-CDMA (Wideband-CDMA) scheme is adopted. In addition, AMC (AdaptiveModulation and channel Coding) scheme, ARQ (Automatic Repeat Request)scheme for packets in the MAC layer, fast packet scheduling, and othersare employed for HSDPA (High Speed Downlink Packet Access) in order toachieve higher transmission rates and quality. For example, non-patentdocument 1 describes the AMC scheme, and non-patent document 2 describesthe ARQ scheme.

FIG. 1 is a schematic view illustrating the AMC scheme. Assuming thattransmission power from a base station is constant, in general, it isestimated that a terminal 11 closer to a base station 10 can receivesignals with greater power than a terminal 12 farther from the basestation 10 can. Thus, since it is estimated that the terminal 11 mayhave better channel conditions, a greater modulation level and a highercoding rate are adopted. On the other hand, the terminal 12 can receivesignals with less power than the terminal 11. As a result, since it isestimated that the terminal 12 may have worse channel conditions, asmaller modulation level and a lower coding rate are adopted.

FIG. 2 shows an exemplary combination of different modulation schemes(modulation level) and different channel coding rates. In theillustrated table, the rightmost column represents relative bit rates inthe case of the bit rate being “1” under the modulation scheme M of“QPSK” and the channel coding rate R of “1/3”. For example, if M=“QPSK”and R=“1/2”, the bit rate of ×1.5 is obtained. In general, there is atendency that the higher the bit rate is, the less the reliability is.More specifically, combinations between different modulation schemes andthe coding rates and different amounts indicative of channel states arepredefined in a listing table, and the modulation schemes and others arechanged depending on the channel state if needed. The amount indicativeof the channel state is managed as Channel Quality Indicator (CQI),which is typically SIR (Signal to Interference power Ratio) and SINR ofa received signal.

FIG. 3 is a schematic view for explaining the ARQ (more accurately,hybrid ARQ). The hybrid ARQ scheme is a technique derived from acombination of the ARQ scheme of requesting retransmission of packetsdepending on results of error detection (CRC: Cyclic Redundancy Check)and some error correction coding scheme (also referred to as channelcoding) for error correction. As illustrated, a CRC bit is added to atransmission data sequence S1), and the resulting signal is sent aftercompletion of error correction encoding (S2). In response to receipt ofthe signal, error correction decoding (also referred to as “channeldecoding”) is carried out (S3), and error detection is carried out (S4).If some error is detected, retransmission of the packet is requested tothe transmitting side (S5). As illustrated in FIG. 4, there are severalmethods for such retransmission.

In an exemplary method illustrated in FIG. 4A, packet P1 is sent fromthe transmitting side to the receiving side. If some error is detectedat the receiving side, the packet P1 is discarded and then theretransmission is requested. In response to the retransmission request,the transmitting side resends the same packet (represented as “P2”) asthe packet P1.

In an exemplary method illustrated in FIG. 4B, packet P1 is sent fromthe transmitting side to the receiving side. If some error is detectedat the receiving side, the receiving side keeps the packet P1 withoutdiscarding it. In response to the retransmission request, thetransmitting side resends the same packet (represented as “P2”) as thepacket P1. Then, the receiving side generates packet P3 by combining thepreviously received packet with the currently received packet. Since thepacket P3 corresponds to one transmitted with double the power of packetP1, the demodulation accuracy is improved.

Also in an exemplary method illustrated in FIG. 4C, packet P1 is sentfrom the transmitting side to the receiving side. If some error isdetected at the receiving side, the receiving side keeps the packet P1without discarding it. In response to the retransmission request, thetransmitting side sends redundancy data derived by performing certainoperations on the packet P1 as packet P2. For example, assume that asequence of packets such as “P1, P1′, P1″, . . . ” has been derived byencoding the packet P1. The derived sequence is predefined as a“puncture pattern”, and may differ depending on the adopted codingalgorithms. In the illustrated example, in response to receipt of aretransmission request, the transmitting side sends P1′ as packet P2.The receiving side generates packet P3 by combining the previouslyreceived packet with the currently received packet. Since the packet P3has increased redundancy, the demodulation accuracy will be improved.For example, assuming that the coding rate of the packet P1 is equal to“1/2”, the coding rate of the packet P3 becomes equal to “1/4”, therebyresulting in improved reliability. Note that the receiving side mustalready know some information as to what coding algorithm is adopted,what redundancy data are sent (puncture pattern), and others.

Fast packet scheduling scheme is a technique intended to improvefrequency utilization efficiency in downlink. In a mobile communicationenvironment, the channel condition between a mobile station (user) and abase station varies over time. In this case, even though transmission ofa large amount of data to a user with a poor channel condition isattempted, it is hard to improve the throughput. On the other hand, thehigher throughput would be achieved for a user with a good channelcondition. From such a viewpoint, it is possible to improve thefrequency utilization efficiency by determining whether the channelcondition is good for each user and assigning a shared data packet infavor of the user with the better channel condition.

FIG. 5 is a schematic diagram for explaining the fast packet schedulingscheme. As illustrated, a shared data packet is assigned to a user withthe better channel condition (a user associated with greater SINR) ineach time slot. As illustrated in FIG. 6, plural codes may be used tomultiplex data destined for different users within a single time slot(frame) in assignment of a shared data packet. In the illustratedexample, codes #1-#10 are used, and in the third frame of five frames,two types of data are multiplexed for user #1 and user #2.

Non-patent document 1: T. Ue, S. Aampei, N. Morinaga and K. Hamaguchi,“Symbol Rate and Modulation Level-Controlled AdaptiveModulation/TDMA/TDD System for High-Bit-Rate Wireless DataTransmission”, IEEE Trans. VT, pp. 1134-1147, vol. 47, No. 4, November1998

Non-patent document 2: S. Lin, Costello, Jr. and M. Miller,“Automatic-Repeat-Request Error Control Schemes”, IEEE CommunicationMagazine, vol. 12, No. 12, pp. 5-17, December 1984

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

In this technical field, there is a strong need for improved speed andcapacity of radio transmission, and in a future communication system, itmay be required to use a wider frequency band than in current systems.However, the wider is the frequency band is used for radiocommunication, the more adverse are the frequency selective fadingeffects due to multipath fading. FIG. 19 schematically shows thereception level of a signal affected by the frequency selective fading.As illustrated in FIG. 19A, if a relatively narrow frequency band isused for radio transmission, the reception level within the frequencyband can be considered to be constant. As illustrated in FIG. 19B, onthe other hand, if a wider frequency band is used, the reception levelshows significant frequency dependence. Hence, it may be advantageousfor improvement of speed and capacity to divide the entire radio bandinto plural frequency blocks and apply AMC, ARQ and packet schedulingfor each frequency block. In the case where these controls are totallycarried out in minimum data units, however, a large number of controlsignals are required, and data transmission efficiency may become worse.

One object of the present invention is to provide a transmissionapparatus and a transmission method enabling control signals requiredfor improved frequency utilization efficiency to be transmittedefficiently in a communication system where data transmission is carriedout in favor of a communicating opponent with a better channelcondition.

Means for Solving the Problem

In order to solve the problem, the present invention relates to atransmitter transmitting data to a communicating opponent with a betterchannel condition with use of one or more frequency blocks including oneor more carrier frequencies. The transmitter includes a communicatingopponent selection unit evaluating channel condition for each frequencyblock for each of plural communicating opponents and selecting one ormore communicating opponents from the plural communicating opponents, amodulation scheme determination unit determining at least a modulationscheme depending on the evaluated channel condition, a control channelgeneration unit generating a control channel indicative of thedetermined modulation scheme and one or more frequency blocks availablefor the selected communicating opponents to receive a data channel, anda channel transmission unit providing the selected communicatingopponents with the control channel and the data channel modulated inaccordance with the modulation scheme.

Advantage of the Invention

According to the embodiment of the present invention, frequencyutilization efficiency can be improved in systems for transmitting datato a communicating opponent with a better channel condition.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view for explaining the AMC scheme;

FIG. 2 is a diagram illustrating exemplary combinations betweendifferent modulation schemes and different channel coding rates;

FIG. 3 is a schematic view for explaining the hybrid ARQ scheme;

FIG. 4 is a diagram illustrating an exemplary transmission scheme;

FIG. 5 is a diagram illustrating reception quality varying over time;

FIG. 6 is a diagram illustrating exemplary code multiplexing for pluralusers;

FIG. 7 is a block diagram of a transmitter according to one embodimentof the present invention;

FIG. 8 is a diagram illustrating exemplary time multiplexing in a radioresource assignment unit;

FIG. 9 is a diagram illustrating exemplary frequency multiplexing in theradio resource assignment unit;

FIG. 10 is a diagram illustrating exemplary code multiplexing in theradio resource assignment unit;

FIG. 11 is a diagram illustrating exemplary radio resource assignmentwith use of plural frequency blocks;

FIG. 12A is a diagram illustrating a transmission procedure in a basestation according to one embodiment of the present invention;

FIG. 12B is a flowchart (1) for explaining the transmission procedure indetail;

FIG. 12C is a flowchart (2) for explaining the transmission procedure indetail;

FIG. 12D is a flowchart (3) for explaining the transmission procedure indetail;

FIG. 13 shows an exemplary table where contents of control informationare listed;

FIG. 14 is a diagram illustrating several examples for illustratingmapping control information and the other information in a downlinkphysical channel;

FIG. 15A is a diagram illustrating an embodiment where controlinformation is mapped per frequency block in a downlink physicalchannel;

FIG. 15B is a diagram illustrating an exemplary localized FDM;

FIG. 15C is a diagram illustrating an exemplary distributed FDM;

FIG. 16 is a diagram illustrating an embodiment where error detectioncoding is performed on control information;

FIG. 17 is a diagram illustrating an embodiment where error correctioncoding is performed in control information;

FIG. 18 shows an exemplary table for comparing different transmissionschemes;

FIG. 19 is a schematic diagram illustrating exemplary frequencyselective fading;

FIG. 20 is a flowchart (1) for explaining an exemplary transmissionprocedure;

FIG. 21 is a flowchart (1)′ for explaining an exemplary transmissionprocedure;

FIG. 22 is a flowchart (2) for explaining an exemplary transmissionprocedure;

FIG. 23 is a flowchart (2)′ for explaining an exemplary transmissionprocedure;

FIG. 24 is a flowchart (2)″ for explaining an exemplary transmissionprocedure;

FIG. 25 is a flowchart (3) for explaining an exemplary transmissionprocedure;

FIG. 26 is a flowchart (1) for explaining an exemplary transmissionprocedure;

FIG. 27 is a flowchart (2) for explaining an exemplary transmissionprocedure;

FIG. 28 is a flowchart (3) for explaining an exemplary transmissionprocedure;

FIG. 29 is a flowchart (1) for explaining an exemplary transmissionprocedure;

FIG. 30 is a flowchart (2) for explaining an exemplary transmissionprocedure;

FIG. 31 is a flowchart (3) for explaining an exemplary transmissionprocedure;

FIG. 32 is a block diagram illustrating a transmitter according to oneembodiment of the present invention;

FIG. 33 is a diagram illustratively showing an exemplary correspondencebetween different modulation schemes and different transmission powerlevels;

FIG. 34 is a diagram illustratively showing an exemplary correspondencebetween different MCS numbers and different transmission power levels;

FIG. 35A is a diagram illustrating transmission power levels ofdifferent resource blocks in case of a conventional AMC control;

FIG. 35B is a diagram illustrating transmission power levels ofdifferent resource blocks in case of AMC control and transmission powercontrol according to an embodiment of the present invention;

FIG. 36 is a schematic diagram illustrating an exemplary relationshipbetween throughputs achievable in MCS1, MCS2, MCS3 and differentsignal-to-noise ratios;

FIG. 37 is a schematic diagram illustrating exemplary assignment ofresource blocks;

FIG. 38 is a diagram illustrating exemplary transmission power levels ofindividual resource blocks; and

FIG. 39 is another diagram illustrating exemplary transmission powerlevels of individual resource blocks.

LIST OF REFERENCE SYMBOLS

10: base station

11, 12: terminal

702: radio resource assignment unit

704: inverse fast Fourier transform unit

706: guard interval insertion unit

720: common control channel processing unit

740: shared control channel processing unit

760: shared data channel processing unit

761: packet scheduling unit

722, 742, 762: channel coding unit

724, 744, 764: data modulation unit

726, 746, 747, 766: data spreading unit

745: control information division-unit

768: power control unit

BEST MODE FOR CARRYING OUT THE INVENTION

In one embodiment of the present invention, the channel condition oneach of plural communicating opponents is evaluated for each frequencyblock. Based on the evaluation, one or more communicating opponents areselected, and at least a modulation scheme is determined depending onthe evaluated channel condition. Then, a control channel is generatedfor indicating the determined modulation scheme and one or morefrequency blocks available for the selected communicating opponents toreceive data, and the control channel and a data channel modulated inaccordance with the determined modulation scheme are provided ortransmitted to the selected communicating opponents. The modulationscheme is allowed to be identified with a lesser number of bits,resulting in a considerable influence on data transmission efficiency.As a result, it is possible to transmit control information to a mobilestation efficiently and thus further improve frequency utilizationefficiency in a communication system that uses a wider frequency bandfor packet scheduling and AMC control.

The channel coding rate may be determined depending on the channelcondition for each frequency block. Also, a data channel and a controlchannel, which have been modulated in accordance with the determinedmodulation scheme and encoded at the channel coding rate, may beprovided or transmitted. The channel coding rate may be determined foreach frequency block. As a result, AMC can be carried out for eachfrequency block.

From the viewpoint of control simplification, the channel coding ratemay be set to a uniform value over plural frequency blocks. The reasonis that the channel coding rate has less influence on data transmissionefficiency than modulation level.

Reception means for receiving a transmission request for data from acommunicating opponent may be provided in a transmitter, andtransmission means may retransmit data in response to a retransmissionrequest. The retransmission of data in response to the retransmissionrequest may be carried out for each frequency block. As a result,retransmission control is achieved for each frequency block.

Error correction coding means for performing error correction coding ona control channel may be provided for hybrid ARQ. The error correctioncoding may be performed for the control channel for each frequency blockfrom the viewpoint of reduced error occurrence. Among control channels,control information on a physical layer and control information on somelayers above the physical layer may be error correction encodedseparately.

In order to address some problems such as that a communicating opponentmay perform unsuitable operation inadvertently, data transmitted fromthe transmission means may include an error detection code for controlinformation. An error detection code may be attached to two types ofcontrol information for the physical layer and its upper layerseparately.

FIRST EMBODIMENT

Although systems adopting the OFDM (Orthogonal Frequency DivisionMultiplexing) scheme in the downlink are focused on in an embodimentpresented below, the present invention may be applied to othermulticarrier types of systems. A wide downlink frequency band may bedivided into plural frequency blocks. A single frequency block maygenerally include one or more carriers. It is assumed in this embodimentthat plural subcarriers are included in each frequency block. Such afrequency block may be also referred to as a resource block or a chunk.A frequency block or a chunk may be used as unit of assignment of radioresources.

FIG. 7 shows a transmitter 700 according to one embodiment of thepresent invention. The transmitter 700 is typically provided in a basestation of a mobile communication system as described in thisembodiment, but it may be provided in other apparatuses. If not statedspecifically, it is assumed that a base station and a transmitter may beused equivalently hereinafter. In FIG. 7 illustrating a portion of thetransmitter 700, a common control channel processing unit 720, a sharedcontrol channel processing unit 740, a shared data channel processingunit 760, a radio resource assignment unit 702, an inverse Fouriertransform unit 704 and a guard interval processing unit 706 areillustrated.

The common control channel processing unit 720 conducts channelencoding, modulation and spreading for transmitting shared controlchannels. A shared control channel includes certain information such asa base station scramble code.

The shared control channel processing unit 740 conducts encoding,modulation and spreading for transmitting shared control channels. Ashared control channel includes certain information such as schedulinginformation for a mobile station to demodulate a shared data channel.

The common control channel processing unit 720 includes a channelencoding unit 722, a data modulation unit 724 and a spreading unit 726.Also, the shared control channel processing unit 740 includes a channelencoding unit 742, a data modulation unit 744 and a spreading unit 746.

The channel encoding units 722 and 742 encode incoming signals inaccordance with a certain coding algorithm and supply the encodedsignals. In the channel encoding units, for example, convolution codingmay be conducted.

The data modulation units 724 and 744 modulate incoming signals andsupply the modulated signals. In the data modulation units, for example,some modulation schemes such as QPSK may be carried out.

The spreading units 726 and 746 spread incoming signals and supply theresulting signals.

The shared data channel processing unit 760 conducts packet-schedulingas well as channel encoding, modulation and spreading on shared datachannels (transmitted data). The shared data channel processing unit 760includes a packet scheduling unit 761, a data modulation unit 764 and aspreading unit 766.

The packet scheduling unit 761 receives individual data items to betransmitted to one or more mobile stations, and schedules the datatransmission based on feedback information and others supplied from therespective mobile stations. The data to be transmitted to the mobilestations are received from upper devices or networks other than a basestation, and are separately stored in a transmission buffer (not shown)for the respective mobile stations. The feedback information includes achannel quality indicator (CQI) measured in each mobile station, and theCQI is represented as SIR in this embodiment. The packet scheduling unit761 evaluates the channel condition for each mobile station based on thechannel quality indicator CQI reported from the mobile station, andselects a mobile station(s) with a better channel condition. As statedbelow, the channel quality indicators CQIs supplied from mobile stationsare reported for each frequency block (or chunk). The packet schedulingunit 761 determines a combination (MCS number) of a modulation schemeand a channel coding rate corresponding to downlink data transmissionbased on the channel quality indicators CQIs supplied from therespective mobile stations. The MCS number may be determined inaccordance with a table as illustrated in FIG. 2. Also, the packetscheduling unit 761 conducts operations associated with packetretransmission based on the feedback information. Information items suchas selected mobile stations, the MCS number and retransmission controlinformation are supplied as control information to the shared controlchannel processing unit 740. Data to be transmitted to the selectedmobile stations are supplied as transmitted data to the channel encodingunit 762.

The channel encoding unit 762 encodes incoming signals in accordancewith a certain coding algorithm, and supplies the encoded signals. Inthe channel encoding unit, for example, turbo encoding may be carriedout.

The data modulation unit 764 modulates incoming signals and supplies themodulated signals. In the data modulation unit, for example, varioustypes of modulation schemes such as QPSK, 16QAM and 64QAM may be used.

The spreading unit 766 spreads incoming signals and supplies the spreadsignals.

The radio resource assignment unit 702 multiplexes signals spread for acommon control channel, a shared control channel and a shared datachannel for output. This multiplexing may be carried out in accordancewith any of time multiplexing, frequency multiplexing and codemultiplexing and any combination thereof. FIG. 8 shows exemplary timemultiplexing of two signals. In this illustration, “channel #1” and“channel #2” represent any two of a common control channel, a sharedcontrol channel and a shared data channel. Although multiplexing of twosignals is illustrated therein for simplicity, three signals may be timemultiplexed. FIG. 9 shows exemplary frequency multiplexing of twosignals, and FIG. 10 shows exemplary code multiplexing of two signals.An appropriate radio resource (a time slot, a frequency band and/or acode) may be assigned to a common control channel, a shared controlchannel and a shared data channel through some multiplexing in the radioresource assignment unit 702 of FIG. 7.

The inverse Fourier transform unit 704 conducts inverse fast Fouriertransform (IFFT) on incoming signals for modulation in accordance withthe OFDM scheme, and supplies the modulated signals.

The guard interval processing unit 706 adds a guard interval to anincoming signal, and generates a symbol in compliance with the OFDMscheme (OFDM symbol) for output. The OFDM symbol is supplied to a radiounit (not shown) for radio transmission.

FIG. 11 is a schematic diagram for explaining an exemplary operation ofa transmitter according to one embodiment of the present invention. Asstated above, a wide downlink frequency band is divided into pluralfrequency blocks or chunks. In this embodiment, each frequency blockincludes plural subcarriers. In this embodiment, radio resources areassigned not only for each time slot (referred to as “transmission slot”in the illustration) but also for each frequency block. As stated below,such a time slot may consist of one transmission time interval (TTI) orany packet time duration. In the illustrated example, the overalldownlink frequency band is divided into eight frequency blocks whereeach of the frequency blocks includes the same number of subcarriers.For each of the eight frequency blocks, the channel condition ismonitored, and the frequency block is assigned for a mobile station witha better channel condition.

FIG. 12A is a flowchart illustrating an exemplary transmission procedurein a base station. At step S121, the base station receives channelquality indicators CQIs from one or more mobile stations, and analyzesthe received channel quality indicators CQIs. The channel qualityindicators CQIs such as reception SIRs are reported for each frequencyblock. In this case, prior to starting this flow, the mobile stationsmeasure quality of a received signal such as a pilot signal, andevaluate the downlink channel condition for each frequency block.

At step 122, it is determined which mobile station has a better channelcondition for each frequency block based on the reception SIR reportedfor the frequency block, and a mobile station with the best receptionSIR in the reported reception SIRs is selected for the frequency block.In addition, a combination (MCS number) of a modulation scheme and achannel coding rate corresponding to the reception SIR is determined.This determination of the combination may be made for each frequencyblock. These steps S121 and S122 are mainly carried out in the packetscheduling unit 761 of FIG. 7. Although the modulation scheme may bedetermined for each frequency block as stated below, a uniform channelcoding rate may be used for plural frequency blocks.

At step S123 of FIG. 12A, a common control channel, a shared controlchannel and a shared data channel are generated. These generations arecarried out in the respective processing units 720, 740 and 760 in FIG.7. Note that the respective channels do not have to be generatedsimultaneously in this step. The shared control channel is generatedbased on control information supplied from the packet scheduling unit761 in FIG. 7. This control information includes some information (MCSnumber etc.) required to demodulate the shared data channel.Specifications of the control information and transmission methodsthereof will be described below.

At step S124 in FIG. 12A, an OFDM symbol is generated. This generationis mainly carried out in the radio resource assignment unit 702, theIFFT unit 704 and the guard interval insertion unit 706.

At step S125 in FIG. 12A, for the selected mobile station at step S122,downlink data transmission is carried out in one or more frequencyblocks in accordance with the determined MCS number.

FIG. 12B is a flowchart for explaining exemplary detailed operations ofthe steps S123 and S124 in FIG. 12A. At step S1, an error detection bitis added to a sequence of transmitted data. Although a cyclic redundancycheck (CRC) bit is added in the illustration, other correction detectionbits may be added.

At step S2, channel encoding is performed. As stated above, the channelencoding is carried out in the channel encoding units 722, 742 and 762in FIG. 7, and particularly, the channel encoding for data channels iscarried out in the channel encoding unit 762.

At step S3, some operation involved in hybrid ARQ is performed. Morespecifically, an information item is generated for indicating whether atransmitted packet is either a packet to be retransmitted or a newpacket, and additionally, other information items may be generated foridentifying the redundancy version of a retransmitted packet. Thisredundancy version can be modified through puncturing or repetition.Also, the channel coding rate may be modified at this step.

At step S4, in assignment to a physical channel, the encoded symbol isassigned for each frequency block. This assignment is mainly carried outin the radio resource assignment unit 702 in FIG. 7. By frequencyscheduling, it is determined for what frequency block the symbol ofwhich user should be assigned.

At steps S5-1 to S5-N (N represents the total number of frequencyblocks), in order to generate a transmission symbol, data modulation isperformed for each frequency block. Subsequently, some operation (notshown) is carried out for radio transmission of the transmission symbol.

In the illustration of FIG. 12B, one modulation scheme is determined foreach frequency block, and different transmission rates suitable for therespective frequency blocks may be set. Thus, the illustrated operationis preferred from the viewpoint of improved transmission throughput.

In the illustration in FIG. 12C, the steps S1 to S4 are the same asthose in FIG. 12B except that step S5′ is uniformly carried out oversome frequency blocks. At step S5′, a uniform modulation scheme isdetermined for all frequency blocks. More generally, such a uniformmodulation scheme may be determined for plural frequency blocks. In thecase where such a uniform modulation scheme is used for plural frequencyblocks, it is possible to reduce the number of control bits (informationamount) required to report the modulation scheme to the receiver sidecompared to the case of FIG. 12B.

As illustrated in FIG. 12D, not only the modulation scheme but also thechannel coding rate may be determined for each frequency block. Notethat signal transmission may preferably be carried out in accordancewith any of the schemes illustrated in FIGS. 12B and 12C in order tosimplify the associated operation and encode data for differentfrequency blocks with the same accuracy.

In the illustration in FIG. 11, user #1 is selected for a certaintransmission slot of frequency block #1 including the lowest subcarrier,and user #2 is selected for the next transmission slot. This means thatuser #1 has the best channel condition in the first transmission slot ofthe frequency block and user #2 has the best channel condition in thenext transmission slot. By determining a mobile station with the bestchannel condition for each transmission slot in each frequency block andperforming data transmission adaptively in accordance with a modulationsuitable for the mobile station, efficient utilization of a widefrequency band is achieved.

FIG. 13 shows primary items of control information supplied to theshared control channel processing unit 740 by the packet scheduling unit761 in FIG. 7 in detail. As illustrated in the leftmost column “FIELDNAMES” in the illustration, the control information includes chunkallocation information, modulation scheme information, coding rateinformation, hybrid ARQ process information, redundancy version, packetstatus information and UE identity.

The chunk allocation information specifies what frequency block isassigned for which mobile station (user). The number of frequency blocksassigned for a certain mobile station (user) may be determined dependingon a requested data rate, and may be greater than or equal to 1 ingeneral. In the illustration in FIG. 11, user #1 is assigned to twofrequency blocks #1 and #4 in the first transmission slot, and each ofuser #2 to user #6 and user #8 is assigned to one frequency block. Inthe subsequent transmission slot, each user is assigned to one frequencyblock. Such assignment to frequency blocks is described in the chunkallocation information. This information belongs to control informationfor the physical layer. Since it is described in this information how toallocate plural frequency blocks, the information does not have to bereported to the individual mobile stations for each frequency block.

The modulation scheme information specifies modulation schemes for usein downlink data transmission, and is identified by the MCS number.Here, various types of multilevel modulation schemes such as QPSK,16QAM, 64QAM and 128QAM may be employed. This information belongs tocontrol information for the physical layer. The information ispreferably reported to mobile stations for each frequency block, but maybe reported for plural frequency blocks.

The coding rate information specifies channel coding rates for use indownlink data transmission, and may be identified by the MCS number. Forexample, the channel coding rate may be specified by a multiple such as1/8=0.125. This information belongs to control information for the layer2 above the physical layer. The channel coding rate may be managed foreach modulation scheme as well as for each frequency block, and may bereported to mobile stations for each frequency block. On the other hand,the channel coding rate may be managed apart from the modulation scheme,and a uniform channel coding rate may be employed over plural frequencyblocks. In FIG. 13, “REQUIRED” of the rightmost column corresponds tothe former case, whereas “NOT REQUIRED” corresponds to the latter case.

The hybrid ARQ process information specifies a packet number associatedwith retransmission control. This information belongs to controlinformation for the layer 2. A packet may be retransmitted for eachfrequency block in accordance with the hybrid ARQ. Alternatively, apacket may be retransmitted for each transmission slot withoutdistinguishing between different frequency blocks. In FIG. 13,“REQUIRED” of the rightmost column corresponds to the former case,whereas “NOT REQUIRED” corresponds to the latter case.

The redundancy version specifies what puncture pattern is used inretransmission control. This information belongs to control informationfor the layer 2. Similar to the hybrid ARQ process information,redundancy data may be transmitted for each frequency block.Alternatively, the redundancy data may be transmitted for eachtransmission slot without distinguishing between different frequencyblocks. In FIG. 13, “REQUIRED” of the rightmost column corresponds tothe former case, whereas “NOT REQUIRED” corresponds to the latter case.

The packet status information specifies whether a packet transmittedfrom a base station to a mobile station is a newly transmitted packet(new packet) or a retransmitted packet. This information belongs tocontrol information for the layer 2. A packet may be retransmitted foreach frequency block in accordance with the hybrid ARQ. Alternatively,it may be retransmitted for each transmission slot withoutdistinguishing between different frequency blocks. In FIG. 13,“REQUIRED” of the rightmost column corresponds to the former case,whereas “NOT REQUIRED” corresponds to the latter case.

The UE identity identifies which mobile station or user receives datatransmitted in the downlink, and is also called a user identifier oridentification information. This information belongs to controlinformation for the physical layer. Similar to the chunk allocationinformation, the UE identity does not have to be reported to mobilestations for each frequency block.

FIG. 14 shows exemplary mapping of a control channel and the otherchannels in downlink physical channels. In configuration 1, the controlchannel is mapped or multiplexed in a certain frequency range over theentire time duration. The frequency range may or may not be the same asthe frequency block range. In configuration 2, the control channel ismapped in the overall frequency range in a certain time duration. Inconfiguration 3, the mappings of configurations 1 and 2 are combined. Inthe configuration 3, the control channel is mapped to certain frequencyranges over a certain time duration. In general, as the control channelis more widely mapped in the frequency direction, frequency diversityhas more advantage, which is desirable from the viewpoint of improvementof reception quality of signals.

In configuration 4, the control channel is mapped to every frequencyblock in the downlink physical channel. The control channel may have avariable data size depending on the number of users or the number offrequency blocks. So, if all channels are mapped in accordance with theconfiguration 2, the control channel occupies variable duration, whichmay complicate demodulation. By combining the configuration 2 with theconfiguration 4, for example, control channels associated with allfrequency blocks (unspecified control channels) are mapped to the entirefrequency range as in the configuration 2, and thereby a control channelspecific to a certain frequency block (specified control channel) onlycan be mapped to the frequency block. As a result, the efficiency andquality of demodulation of the control channels is improved. In order tomap a control channel for each frequency block, as illustrated in FIG.15A, it is desirable to provide a control information division unit 745for separating the control channel associated with a certain frequencyblock from the other control channels.

The mapping configurations as illustrated in FIG. 14 are simplyillustrative, and the control channel and the other channels may bemultiplexed in various schemes including single time multiplexing,frequency multiplexing or code multiplexing or any combination thereof.In addition, the multiplexing is not limited to the control channel andthe other channels, and may be performed on any channels. For example,in case of multiplexing of data channels for individual users, variousmodulation schemes may be employed. As one example, each of plural usersmay be assigned to one or more frequency blocks, and the modulationscheme may be determined in such a manner as illustrated in FIG. 12B. Inthe example illustrated in FIG. 15B, each of four users may be assignedto a frequency block, and different modulation schemes may be set foreach of the frequency blocks. Alternatively, a uniform modulation schememay be determined over plural frequency blocks as illustrated in FIG. 12C. The multiplexing in the frequency direction as illustrated in FIG.15B is referred to as a localized frequency division multiplexing(localized FDM) scheme due to a certain band being occupied by a certainuser. On the other hand, a scheme for distributing a channel associatedwith a certain user over a wideband is referred to as a distributed FDMscheme. In the latter scheme, each channel includes plural frequencycomponents (subcarrier components) assigned in a uniform or non-uniforminterval on the frequency axis, and different channels are madeorthogonal with each other in the frequency range. In the illustrationin FIG. 15C, channels of individual users are distributed over the wholesystem band, and are made orthogonal with each other in the frequencyrange.

At least one of a modulation scheme and a channel coding rate may bedetermined for each frequency block or may be determined for pluralfrequency blocks uniformly. Also, they may be determined in furthersmaller frequency units. Thus, according to the multiplexing asillustrated in FIG. 15C, a modulation scheme may be determined for eachsubcarrier. Even if the modulation scheme is determined in such asmaller unit, however, it is estimated that the throughput cannot be somuch improved. Also, since additional control channels for identifyingall of them are required, there is a risk of increasing the processingworkload and the amount of control information. On the other hand,according to the distributed FDM, the frequency diversity has moreadvantage, and thus improved signal quality can be expected. Therefore,in the case of the distributed FDM, it is desirable that the modulationscheme and the channel coding rate be uniformly determined over allsubcarriers, resulting in a reduced amount of control information.

FIG. 16 shows exemplary error detection encoding on a control channel.The error detection encoding may be carried out, for example, with theuse of cyclic redundancy check CRC code. The error detection encodingmakes it possible to prevent a user from demodulating data for anotheruser and performing erroneous retransmission control, for example. Inthe illustration in FIG. 16A, control information for physical layer andcontrol information for the upper layer 2 are separately error detectionencoded. It is advantageous in terms of mapping per frequency block likethe configuration 4 in FIG. 14 to conduct error detection encodingdepending on the type of the control information. In the illustration inFIG. 16B, control information for the physical layer and the controlinformation for the upper layer 2 may be error detection encodedtogether. Compared to the case where the error detection encodings areseparately carried out, this scheme is advantageous due to reducedoverhead. Preferably, they are error detection encoded separately toimprove error detection capability and fulfill a smaller retransmissionunit as illustrated in FIG. 16A.

FIG. 17 shows exemplary error correction encoding on controlinformation. The error correction encoding may be carried, for example,by use of convolution encoding. The error correction encoding mayimprove tolerance over multipath fading, for example. In theillustration in FIG. 17A, the control information for the physical layerand the control information for the upper layer 2 are error correctionencoded separately. In the illustration in FIG. 17B, the controlinformation for the physical layer and the control information for theupper layer 2 are error correction encoded together. In other words,error correction encoding is performed on the overall controlinformation. This is desirable from the viewpoint of reduced overhead.In addition, the error correction capability (encoding gain) isadvantageous to the case (B) of a longer coding unit. However, such alonger coding unit may cause chaining of a bit error to subsequent bits.In other words, the longer coding unit may tend to increase the erroroccurrence probability. In fact, the coding unit may be determined bybalancing these characteristics.

FIG. 18 shows an exemplary table for listing various methods where oneor more of frequency range based packet scheduling, adaptive modulationcoding (AMC) and hybrid ARQ are carried out for each frequency block. Inone row, some features of one method are illustrated.

In the method 1, all of the frequency range based packet scheduling,data modulation, the channel coding rate and hybrid ARQ are controlledfor each frequency block. In this manner, frequency resources can beutilized most efficiently, resulting in extremely efficient datatransmission. However, many of the control information items listed inFIG. 13 have to be managed for each frequency block, resulting inconsiderably increasing the overhead. More specifically, all ofmodulation scheme information, coding rate information, hybrid ARQprocess information, redundancy version and packet status informationare reported to mobile stations for each frequency block.

In the column “CHARACTERISTICS” in the table, the symbol double circle“⊚” indicates that the data transmission is extremely efficient. Thesymbol circle “◯” indicates that the data transmission is veryefficient. The symbol triangle “Δ” indicates that the data transmissionis moderately efficient. The symbol cross “×” indicates that the datatransmission is inefficient. Also in the column “OVERHEAD” in the table,the symbol double circle “⊚” indicates that the overhead is very low.The symbol circle “◯” indicates that the overhead is low. The symboltriangle “Δ” indicates that the overhead is high. The symbol cross “×”indicates that the overhead is very high. Note that the symbols usedherein simply indicate tendency of relative merits and the availabilityis not necessarily determined.

In the method 2, the frequency range based packet scheduling, the datamodulation and the hybrid ARQ are controlled for each frequency block,whereas the channel coding rate is controlled for each transmission timeinterval TTI. The transmission time interval is a constant unit timespecific to a system. In the method 2, only the channel coding rate isset to have a uniform value over all frequency blocks. Thus, the method2 achieves reduction in overhead compared to the method 1 in that thechannel coding rate does not have to be managed for each frequencyblock. More specifically, the modulation scheme information, the hybridARQ process information, the redundancy version and the packet statusinformation are reported to mobile stations for each frequency block,whereas a uniform coding rate information over all frequency blocks isreported.

In the method 3, the frequency range based packet scheduling, the datamodulation and the hybrid ARQ are controlled for each frequency block,whereas the channel coding rate is controlled for each packet. Thelength (duration) of a packet may be a relative amount defined in anupper network, for example, it may or may not be the same as absoluteunit time (TTI) specific to a system. In the method 3, only the channelcoding rate is set to have a uniform value over all frequency blocks.Thus, the method 3 can also reduce the overhead compared to the method 1in that the channel coding rate does not have to be managed for eachfrequency block. More specifically, the modulation scheme information,the hybrid ARQ process information, the redundancy version and thepacket status information are reported to mobile stations for eachfrequency block, whereas uniform coding rate information over allfrequency blocks is reported. Note that the coding rate information hasto be reported for each packet.

In the method 4, the frequency range based packet scheduling, the datamodulation and the channel encoding are controlled for each frequencyblock, whereas the hybrid ARQ is controlled for each packet. In otherwords, retransmission is controlled without distinguishing betweendifferent frequency blocks, resulting in reduced overhead accordingly.Also, the length of a packet is equal to one unit of actuallycommunicated information, and retransmission is carried out for eachpacket. This is preferable from the viewpoint of improvement of thethroughput. More specifically, the modulation scheme information and thecoding rate information are reported to mobile stations for eachfrequency block, whereas the hybrid ARQ process information, theredundancy version and the packet status information are reporteduniformly over all frequency blocks. Note that information associatedwith retransmission control has to be reported for each packet.

In the method 5, the frequency range based packet scheduling and thedata modulation are controlled for each frequency block, the channelcoding is controlled for each transmission time interval, and the hybridARQ is controlled for each packet. In other words, the channel codingrate and retransmission are controlled without distinguishing betweendifferent frequency blocks, resulting in reduced overhead accordingly.More specifically, the modulation scheme information is reported tomobile stations for each frequency block, whereas the coding rateinformation, the hybrid ARQ process information, the redundancy versionand the packet status information are reported uniformly over allfrequency blocks. Note that information associated with retransmissioncontrol has to be reported for each packet.

In the method 6, the frequency range based packet scheduling and thedata modulation are controlled for each frequency block, whereas thechannel coding rate and the hybrid ARQ are controlled for each packet.In other words, the channel coding rate and retransmission arecontrolled without distinguishing between different frequency blocks,resulting in reduced overhead accordingly. More specifically, themodulation scheme information is reported to mobile stations for eachfrequency block, whereas the coding rate information, the hybrid ARQprocess information, the redundancy version and the packet statusinformation are reported uniformly over all frequency blocks. Note thatsome information associated with the coding rate and the retransmissioncontrol has to be reported for each packet.

In the method 7, the frequency range based packet scheduling, the datamodulation and the channel coding are controlled for each frequencyblock, whereas the hybrid ARQ is controlled for each transmission timeinterval TTI. In other words, only the retransmission is controlledwithout distinguishing between different frequency blocks. The method 7can reduce overhead in that the retransmission does not have to becontrolled for each frequency block. Also, since the retransmission iscarried out for each transmission time interval TTI regardless of thepacket length, the retransmission control can be simplified. Morespecifically, the modulation scheme information and the coding rateinformation are reported to mobile stations for each frequency block,whereas the hybrid ARQ process information, the redundancy version andthe packet status information are reported uniformly over all frequencyblocks. Note that some information associated with the retransmissioncontrol has to be reported for each transmission time interval TTI.

In the method 8, the frequency range based packet scheduling and thedata modulation are controlled for each frequency block, whereas thechannel coding and the hybrid ARQ are controlled for each transmissiontime interval. In other words, the channel coding rate and theretransmission are controlled without distinguishing between differentfrequency blocks, resulting in reduced overhead accordingly. Morespecifically, the modulation scheme information is reported to mobilestations for each frequency block, whereas the coding rate information,the hybrid ARQ process information, the redundancy version and thepacket status information are reported uniformly over all frequencyblocks. Note that some information associated with the coding rateinformation and the retransmission control has to be reported for eachtransmission time interval.

In the method 9, the frequency range based packet scheduling and thedata modulation are controlled for each frequency block, the channelcoding is controlled for each packet, and the hybrid ARQ is controlledfor each transmission time interval. In other words, the channel codingrate and the retransmission control are controlled withoutdistinguishing between different frequency blocks, resulting in reducedoverhead accordingly. More specifically, the modulation schemeinformation is reported to mobile stations for each frequency block,whereas the coding rate information, the hybrid ARQ process information,the redundancy version and the packet status information are reporteduniformly over all frequency blocks. Note that the coding rateinformation has to be reported for each packet and that some informationassociated with the retransmission control has to be reported for eachtransmission time interval.

In the method 10, the frequency range based packet scheduling iscontrolled for each frequency block, whereas the data modulation, thechannel coding and the hybrid ARQ are controlled for each transmissiontime interval. In other words, the data modulation, the channel codingrate and the retransmission are controlled without distinguishingbetween different frequency blocks, resulting in extremely reducedoverhead. More specifically, the modulation scheme information, thecoding rate information, the hybrid ARQ process information, theredundancy version and the packet status information are reporteduniformly over frequency blocks. Note that these information items haveto be reported for each transmission time interval TTI.

In conjunction with the methods 1-10, while the control over modulationschemes (modulation multilevel) has a strong influence on datatransmission efficiency, throughput or frequency utilization, a lesseramount of information is required to specify the modulation schemescompared to the retransmission control information or others. Thus, thedata modulation should be controlled for each frequency block. Bycomparing these methods, on the other hand, we can recognize that thecontrol over the channel coding rate has little influence over the datatransmission efficiency and overhead (characteristics). Thus, it isadvantageous to control the channel coding rate for each transmissiontime interval TTI from the viewpoint of simplified signal processing.The retransmitted unit of the retransmission control ARQ has influenceon the overhead, and it will be understood that higher overhead leads tohigher data transmission efficiency. On the other hand, it is desirableto use an actually communicated information unit as criteria (to controlthe channel coding rate for each packet) rather than the transmissiontime interval TTI from the viewpoint of retransmission efficiency. Notethat the channel coding rate is desirably controlled for eachtransmission time interval TTI from the viewpoint of simplifiedretransmission control.

SECOND EMBODIMENT

According to the first embodiment, attachment of CRC bits, the channelcoding and the retransmission control are carried out for only a singledata sequence. In the second embodiment, the attachment of CRC bits, thechannel coding and the retransmission control are carried out for eachof plural data sequences.

FIG. 20 is a flowchart (1) illustrating an exemplary transmissionprocedure according to one embodiment of the present invention. At stepS1, a sequence of transmitted data is divided into plural sequences. Theoperation on the divided sequences is performed as in the flowchart (1)in FIG. 12B. The division of the data sequence may be carried out, forexample, in a serial to parallel (S/P) conversion unit. The division maybe referred to as partition and segmentation. In any case, the size ofdivided data may be the minimum unit for retransmission. It is desirablethat the size of divided data be made smaller from the viewpoint ofretransmission of minimum required information. On the other hand, it isdesirable that the size of divided data be made larger from theviewpoint of reduction in overhead associated with the retransmission.However, if the size of divided data is too large in the latter case, alarge amount of data may have to be retransmitted due to occurrence of aslight error. Thus, it is desirable that if the data size exceeds acertain upper bound (predefined threshold) in the latter case, thedivision can be triggered. Although it is illustrated in FIG. 20 thatthe transmitted data sequence is divided into two sequences forsimplicity, the transmitted data sequence may be divided into more thantwo sequences. Also, in the case where the division is triggered by thedata size exceeding a threshold, the two lines of flow in FIG. 20 maynot be necessarily conducted simultaneously. (If the data size is small,only one of the left-hand flow and the right-hand flow may beconducted.)

At steps S12 and S22, an error detection bit is attached to each of thedivided transmitted data sequences. The data size of the dividedsequences may or may not be uniform over the sequences.

At steps S13 and S23, each of the divided transmission data sequences ischannel encoded. The channel coding rate R1 for step S13 and the channelcoding rate for step S23 may be determined independently. Also, they maybe set to be different values or the same value.

At steps S14 and S24, an operation associated with hybrid ARQ isperformed on each of the divided transmitted data sequences. Morespecifically, some information is generated for indicating whether apacket to be transmitted is a retransmitted packet or a new packet. Inaddition, some information may be generated for indicating theredundancy version of the transmitted packet and others. The redundancyversion for step S14 and the redundancy version for step S24 may bedetermined independently. Also, they may be set to be different versionsor the same version.

At steps S15 and S25, a physical channel is assigned to each of thedivided transmitted data sequences, and an encoded symbol is assigned toeach frequency block. This operation is mainly conducted in the radioresource assignment unit 702. It is determined in frequency schedulingwhich frequency block is assigned to the symbol of which user.

At steps S16-1 to S16-K and S26-1 to S26-L, data modulation is carriedout for each frequency block for generating a transmission symbol. Notethat K and L represent the total number of frequency blocks in therespective sequences. Subsequently, some operation (not shown) isconducted for radio transmission of the transmission symbol.

In the illustration in FIG. 20, since a modulation scheme is determinedfor each divided sequence for each frequency block, the transmissionrate is set to have a value suitable for each frequency block. Thus, theillustrated exemplary operation is preferable from the viewpoint ofimproved transmission throughput.

FIG. 21 is a flowchart (1)′ illustrating an exemplary transmissionprocedure. This flowchart is the same as FIG. 20 except for step 3. Inthe illustration, the two divided transmitted data sequences areseparately channel encoded, but the respective channel coding rates areset to have a uniform value (R1=R2). Since the same channel coding rateis used for the respective sequences, it is possible to reduce thenumber of control bits required to report the channel coding rate to thereceiver side.

FIG. 22 is another flowchart (2) illustrating a transmission procedure.The operation subsequent to division at step S1 is the same as theflowchart (2) in FIG. 12C. This flow is the same as the flow in FIG. 20except for steps S16′ and S26′. In the illustration, modulation schemesare determined for two divided sequences of transmitted dataindependently, but the same modulation scheme is applied to the samedata sequence. In the illustration in FIG. 20, however, differentmodulation schemes may be applied to different frequency blocks. Sincethe same modulation scheme is applied to plural frequency blocks, it ispossible to reduce the number of control bits required to report themodulation scheme to the receiver side.

FIG. 23 is a flowchart (2)′ illustrating an exemplary transmissionprocedure. This flow is the same as the flow in FIG. 22 except for stepS3. In the illustration, channel coding is performed on the two dividedsequences of transmitted data separately, but the same channel codingrate is set for them (R1=R2). Also, the same modulation scheme isapplied to the same data sequence. Since the same channel coding rate isapplied to the different sequences and the same modulation scheme isapplied to plural frequency blocks, it is possible to reduce the numberof control bits required to report the channel coding rate and themodulation scheme to the receiver side.

FIG. 24 is another flowchart (2)″ illustrating an exemplary transmissionprocedure. This flow is the same as the flow in FIG. 23 except for stepS6. In the illustration, channel coding is performed on the two dividedsequences of transmitted data separately, but the same channel codingrate is set for them (R1=R2). Also, the same modulation scheme isapplied to the data sequences. Since the same channel coding rate isapplied to different sequences and the same modulation scheme is appliedto all frequency blocks, it is possible to further reduce the number ofcontrol bits required to report the channel coding rate and themodulation scheme.

FIG. 25 is another flowchart (3) illustrating an exemplary transmissionprocedure. The operation subsequent to the division at step S1 is thesame as the flowchart (3) in FIG. 12D. Also, this flow is the same asthe flow in FIG. 20 except for steps S13-1 to S13-K and S23-1 to S23-L.In the illustration, channel coding may be performed on each frequencyblock. In order to simplify the operation and decode data for individualfrequency blocks with the similar accuracy, it is preferable to transmitsignals in accordance with the procedures illustrated in FIGS. 20-24.

THIRD EMBODIMENT

The division of a data sequence to be transmitted into plural sequencesmay be conducted by means of various products and applications undervarious processing environments. In the third embodiment of the presentinvention, the data sequence to be transmitted is divided correspondingto plural reception antennas.

FIG. 26 is a flowchart (1) illustrating an exemplary transmissionprocedure according to the third embodiment. Conventionally, a datasequence is finally transmitted from a single transmission antenna.According to the illustration in FIG. 26, divided data sequences aretransmitted from different transmission antennas #1 and #2. Similar tothe case of FIG. 20, the number of divided sequences may be set to be anarbitrary value, that is, any number of transmission antennas may beprovided. In addition, the operation associated with a singletransmission antenna (for example, transmission antenna #1) in FIG. 26may be replaced with any of the operations described in conjunction withFIGS. 20-25. In other words, a data sequence transmitted from a singletransmission antenna may be divided into plural data sequences. In thiscase, such a data sequence to be transmitted is divided into a largernumber of data sequences than the number of transmission antennas.According to the third embodiment, in the case where data transmissionis carried out in accordance with a MIMO multiplex scheme by means of amulti-antenna device with plural transmission antennas, a channel codingrate is set for each of the transmission antennas and a modulationscheme is set for each frequency block. This procedure is preferred fromthe viewpoint of improved throughput.

FIG. 27 is another flowchart (2) illustrating an exemplary transmissionprocedure. This flow is the same as the flow in FIG. 22 except thatdivided different data sequences are transmitted from the differenttransmission antennas #1 and #2. In the illustration, for datatransmitted from the same transmission antenna, the same modulationscheme is applied to plural frequency blocks (all frequency blocks inthe illustration). Thus, it is possible to reduce the number of controlbits required to report the modulation scheme to the receiver side.Since this reducing advantage grows proportionately to the number oftransmission antennas, the number of control bits may be furthersignificantly reduced compared to the second embodiment.

FIG. 28 is another flowchart (3) illustrating an exemplary transmissionprocedure. This flow is the same as the flow in FIG. 25 except thatdivided different data sequences are transmitted from differenttransmission antennas #1 and #2.

FOURTH EMBODIMENT

Similar to the third embodiment, the fourth embodiment of the presentinvention also relates to the multi-antennas scheme.

FIG. 29 is a flowchart (1) illustrating an exemplary transmissionprocedure. The individual steps have been already explained in detail,and thus the duplicative description thereof will be omitted. In thisembodiment, before a data sequence is divided for respectivetransmission antennas, attachment of a CRC bit, channel coding andretransmission control are carried out uniformly over the all thetransmission antennas. As a result, the attachment of a CRC bit and thechannel coding are performed on a packet with a relatively large datasize. Subsequently, this packet is divided and transmitted via thetransmission antennas. According to this embodiment, it is possible toreduce the number of control bits required to report the channel codingrate to the receiver side and provide the CRC bit.

FIG. 30 is a flowchart (2) illustrating an exemplary transmissionprocedure. In this flow, the attachment of a CRC bit, the channel codingand the retransmission control are carried out uniformly over alltransmission antennas as in FIG. 29. However, the same modulation schemeis applied to data transmitted from the same transmission antennaregardless of frequency blocks. Since the same modulation scheme isapplied to plural frequency blocks, it is possible to reduce the numberof control bits required to report the modulation scheme to the receiverside.

FIG. 31 is a flowchart (3) illustrating an exemplary transmissionprocedure. In this flow, the attachment of CRC bits, the channel codingand the retransmission control are carried out uniformly over alltransmission antennas as in FIG. 29. In the illustration, the modulationscheme is not only determined for each frequency block but also thechannel coding rate is determined for each frequency block.

FIFTH EMBODIMENT

As stated above, adaptive modulation coding (AMC) is controlled intransmission of shared data channels. As illustrated in FIG. 1,transmission power is kept constant under the AMC control. That isintended to maintain signal quality by communicating under a combination(MCS) of a modulation scheme and a coding scheme suitable for thechannel condition. In order to maintain good signal quality even undervarious channel conditions, it is desirable to prepare various MCSs asillustrated in FIG. 2. If there are not a sufficient number of MCScombinations, lower data transmission efficiency (throughput) can beachieved particularly under the condition where switching between MCSsis carried out.

On the other hand, for different combinations of modulation schemes andcoding schemes, signal processing (encoding, decoding, modulation,demodulation and others) also differs at the transmitter side and thereceiver side. Thus, if there are a large number of MCSs, the number ofmodification times of signal processing schemes and computationalworkload may also increase. This is not desirable from the viewpoint ofsimplification of the signal processing (particularly for simplecommunication terminals). The fifth embodiment of the present inventioncan address the above-mentioned problem.

FIG. 32 is a block diagram illustrating a transmitter according to thisembodiment. This transmitter is the same as the transmitter describedabove in conjunction with FIG. 7 except that a shared data channelprocessing unit 760 in FIG. 32 includes a power control unit 768.Although some components for setting transmission power for commoncontrol channels and shared control channels may be provided, thesecomponents do not relate to the present invention directly and thus arenot illustrated. Note that the channel coding rate, the modulationscheme and the transmission power are kept constant for the commoncontrol channels. Also for the shared control channels, the channelcoding rate, the modulation scheme and the transmission power are keptconstant in general. The transmission power for the shared controlchannels may be controlled in accordance with open-loop or closed-looptransmission power control or based on reception quality (CQIinformation) of downlink pilot channels reported from mobile stations.

The power control unit 768 adjusts the transmission power for datachannels based on power control information supplied from the packetscheduling unit 761. In this embodiment, the combination of a modulationscheme and a coding scheme for the data channels is adjusted under theAMC control if needed, and in addition, transmission power for datachannels is also controlled. The power control information includesinformation for specifying transmission power of shared data channelsfor each resource block (frequency block). The power control informationis determined by the packet scheduling unit 761. The power controlinformation may be derived based on a correspondence predeterminedbetween modulation schemes (or MCSs) and transmission power levels.Alternatively, the power control information may be found without use ofsuch a predetermined correspondence. The power control information maybe updated for each subframe (or TTI) or may be more or less frequentlyupdated.

FIG. 33 shows an exemplary correspondence available to the case wherethe power control information is derived based on a predefinedcorrespondence. In the illustration, the transmission power P1 is usedin case of the modulation scheme being QPSK. The transmission power P2is used in case of the modulation scheme being 16QAM. The transmissionpower P3 is used in case of the modulation scheme being 64QAM. There maybe some or no relationship among the transmission power levels P1, P2and P3. For example, there may or may not be some ratio relationshipsuch as “P2=2P1 and P3=3P1”. Of course, the data modulation schemesand/or the transmission power levels are not limited to the above threetypes, and may have more or less types. In addition, the modulationscheme and the transmission power may or may not have one-on-onecorrespondence to each other. For example, the same transmission powerP1 may be used for both QPSK and 16QAM. FIG. 34 shows an exemplarycorrespondence between MCSs and transmission power levels. Thecorrespondence is not limited to the illustrations in FIGS. 33 and 34,and any other correspondence may be predefined. It is sufficient thatthe transmission power can be derived from the modulation schemes andothers.

FIGS. 35A and 35B show exemplary transmission power for individualresource blocks. In FIG. 35A, the same transmission power level is setfor all resource blocks, which corresponds to case of transmission powerunder the conventional AMC control. FIG. 35B illustrates an exemplarycase where the AMC control as well as the transmission power level isset for each resource block. Since not only MCSs but also thetransmission power can be adaptively changed, the throughput can befurther improved compared to the case with use of only the AMC control.

FIG. 36 schematically shows an exemplary relationship betweenthroughputs achievable under predefined MCSs and signal-to-noise ratios(SNRs). Suppose that MCS1 has a lower bit rate than MCS2 and in turnMCS2 has a lower bit rate than MCS3. Let the maximum throughputsachievable under MCS1, MCS2 and MCS3 be Tph1, Tph2 and Tph2,respectively. Also, suppose that the SNR under a certain transmissionpower level is equal to the value “E” in the illustration. In this case,the throughput achievable under MCS1 is approximately Tph1, whereasthroughput higher than Tph1 may be achievable under MCS2. However,suppose that MCS2 is not provided in the system and only the MCS1 andMCS3 are provided in the system. In this case, according to theconventional AMC control, when the SNR is equal to E, only MCS1 can beadopted in the system. On the other hand, according to this embodiment,higher transmission power is achieved. For example, it is possible toincrease the SNR from E to F. Once the SNR is equal to F, MCS3 togetherwith MCS1 become available. By using MCS3, higher throughput isachieved. In other words, according to this embodiment, even if only theMCS1 and MCS3 are provided in a system among the three types of MCSs,that is, MCS1, MCS2 and MCS3, higher throughput is achieved. In otherwords, it is possible to use variable transmission power to reduce thekinds of MCSs while maintaining high throughput.

As stated above, the level of transmission power may be derived based ona predefined correspondence between modulation schemes or others andtransmission power levels. Alternatively, it may be found without use ofsuch a predefined correspondence. In the former, power informationindicative of the predefined correspondence is stored as commoninformation between a base station and a mobile station in respectivememories. The mobile station can determine the transmission power for anMCS reported from the base station with reference to the correspondence.In this case, the base station does not have to transmit the informationindicative of the transmission power via shared control channels orothers. The predefined correspondence may be reported to the mobilestation via a common control channel such as broadcast information.Alternatively, the correspondence may be reported to the mobile stationas layer 3 information at call setting time or may be written in ROM assystem specific information.

On the other hand, without such a predefined correspondence, whenassigning individual resource blocks to users, the base station mayderive the transmission power individually so to as facilitate the bestthroughput. Since the MCS as well as the transmission power isoptimized, this method is particularly advantageous to improveachievable throughput. Note that information for indicating whichresource block has been used for transmission via a data channel at whatlevel of the transmission power has to be reported to mobile stationsvia shared control channels.

Also, if the predefined correspondence is not used, the base stationdoes not have to report the transmission power to mobile stations viashared control channels. For example, the mobile stations may measurereception quality of individual resource blocks assigned for themselves,and may estimate the transmission power.

Hence, the frequency of how often assignment status of resource blocks(information indicating which resource blocks are assigned for whichusers) is reported to mobile stations may be reported for each subframe(TTI) or less frequently. More generally, the respective frequency ofreporting to mobile stations may or may not be the same for all or aportion of the resource block assignment status, the MCS number and thetransmission power. A shared control channel may be used for thereporting.

FIG. 37 schematically shows an exemplary assignment of resource blocks.In the illustration, shaded resource areas are assigned for certainusers. In the illustrated example, assignment status of resource blocksis reported to mobile stations every three subframes (resourceassignment report), and the assignment is modified if needed. In otherwords, the resource block assignment status is invariantly maintainedduring the three subframes. Although a resource block is assigned for auser with a better channel condition, there is no guarantee that thegood channel condition is maintained throughout all resource blocksduring the three subframes. In some cases, the channel condition maychange into a worse condition. In the illustration, “×” marked resourceblocks indicate that their channel condition has become worse. The “×”marked resource blocks should not be used as data channels fortransmission. In this embodiment, the transmission power for theseresource blocks may be set to be zero to prevent the resource blocksfrom being used. Thus, even if assignment of the resource blocks isinfrequently updated, unnecessary data transmission can be avoided bysetting the transmission power for resource blocks with poor channelcondition to be zero.

The setting of the transmission power to zero if needed is alsoadvantageous to mobile stations together with efficient utilization ofcommunication resources. This is explained in detail with reference toFIGS. 38 and 39. FIG. 38A schematically shows an exemplary case wheresome data are transmitted at the same transmission power in all theeight resource blocks assigned for certain users. This corresponds tothe case of the conventional AMC control and is the same as FIG. 35A.FIG. 38B shows an exemplary case where the transmission power forrecourse blocks RB3 and RB5 is set to be zero. In this case, it isdesirable that a base station raise the transmission power associatedwith resource blocks other than the resource blocks RB3 and RB5 as wellas keep the total amount of transmission power as constant as possible.This is why the total transmission power level at the base stationshould be maintained as constant as possible from the viewpoint ofstable operation of a power amplifier. As a result, the transmissionpower is raised from P1 to P1′. From the viewpoint of mobile stations,it can be expected that reception quality associated with the resourceblocks other than RB3 and RB5 is improved. FIGS. 39A and 39B showrespective cases before and after the transmission power for theresource blocks RB3 and RB5 being set to zero. In the illustration, thetransmission power is controlled as in the case of FIG. 35B. Asillustrated in FIG. 39B, the transmission power is raised for eachresource block.

Information indicating for which resource block the transmission poweris set to be zero may be reported to mobile stations via any sharedcontrol channels other than shared control channels indicative ofresource block assignment status. However, it is likely that such sharedcontrol channels are not necessarily provided. For example, mobilestations may intend to receive all the resource blocks assigned forthemselves, and may ignore signals for resource blocks with less than apredefined reception quality (in the above example, RB3 and RB5). Whenthe information indicating for which resource block the transmissionpower is equal to zero is reported to a mobile station, the mobilestation can measure reception quality associated with each resourceblock with high accuracy based on the reported information, the totaltransmission power and reception power for the mobile station.

The preferred embodiments of the present invention have been describedabove. However, the present invention is not limited to theseembodiments, and various modification and variations may be made withinthe scope and sprit of the present invention. For convenience, thepresent invention has been described with reference to the distinctembodiments. However, the distinction of the embodiments is notessential to the present invention, and one or more embodiments may beused if needed.

This international patent application is based on Japanese PriorityApplication No. 2005-106908 filed on Apr. 1, 2005, the entire contentsof which are hereby incorporated by reference.

This international patent application is also based on Japanese PriorityApplication No. 2006-9299 filed on Jan. 17, 2006, the entire contents ofwhich are hereby incorporated by reference.

This international patent application is also based on Japanese PriorityApplication No. 2006-31750 filed on Feb. 8, 2006, the entire contents ofwhich are hereby incorporated by reference.

1. A transmitter for assigning a data channel for a communicatingopponent with a better channel condition with use of one or morefrequency blocks including one or more carrier frequencies, comprising:a communicating opponent selection unit evaluating the channel conditionfor each of the frequency blocks for each of plural communicatingopponents and selecting one or more of the communicating opponents fromthe plural communicating opponents; a modulation scheme determinationunit determining at least a modulation scheme depending on the evaluatedchannel condition; a control channel generation unit generating acontrol channel indicative of the determined modulation scheme and oneor more frequency blocks available for the selected communicatingopponents to receive a data channel; and a channel transmission unitproviding the selected communicating opponents with the control channeland the data channel modulated in accordance with the modulation scheme.2. The transmitter as claimed in claim 1, the modulation schemedetermination unit determining a channel coding rate depending on thechannel condition for each of the frequency blocks; the channeltransmission unit transmitting data including the control channel andthe data channel, the data channel being modulated in accordance withthe modulation scheme and encoded with the channel coding rate.
 3. Thetransmitter as claimed in claim 2, wherein the channel coding rate isset to be a uniform value over the plural frequency blocks.
 4. Thetransmitter as claimed in claim 1, wherein the modulation scheme isdetermined for each of the frequency blocks.
 5. The transmitter asclaimed in claim 1, wherein the modulation scheme is determineduniformly over the plural frequency blocks.
 6. The transmitter asclaimed in claim 1, wherein the modulation scheme is determineduniformly over plural subcarriers distributed over a frequency axis. 7.The transmitter as claimed in claim 1, further comprising: aretransmission request reception unit receiving a retransmission requestfor data from one of the communicating opponents, the channeltransmission unit, in response to the retransmission request,retransmitting the data.
 8. The transmitter as claimed in claim 7,wherein the transmission of the data in response to the retransmissionrequest is conducted for each of the frequency blocks.
 9. Thetransmitter as claimed in claim 1, further comprising: an errorcorrection coding unit performing error correction coding on the controlchannel.
 10. The transmitter as claimed in claim 9, the error correctioncoding unit performing the error correction coding on the controlchannel for each of the frequency blocks.
 11. The transmitter as claimedin claim 1, wherein the data transmitted by the channel transmissionunit includes an error detection code for the control channel.
 12. Thetransmitter as claimed in claim 1, further comprising: a division unitdividing a data sequence to be transmitted into plural sequences, themodulation scheme determination unit determining at least a modulationscheme for each of the plural divided sequences.
 13. The transmitter asclaimed in claim 12, the modulation scheme determination unitdetermining the modulation scheme for each of the frequency blocks foreach of the plural divided sequences.
 14. The transmitter as claimed inclaim 12, the modulation scheme determination unit determining a uniformmodulation scheme over the plural frequency blocks for each of theplural divided sequences.
 15. The transmitter as claimed in claim 12,the modulation scheme determination unit determining a uniformmodulation scheme over the plural divided sequences.
 16. The transmitteras claimed in claim 12, the modulation scheme determination unitdetermining a uniform modulation scheme over plural subcarriersdistributed over a frequency axis for each of the plural dividedsequences.
 17. The transmitter as claimed in claim 12, the modulationscheme determination unit further determining a channel coding rate foreach of the plural divided sequences.
 18. The transmitter as claimed inclaim 12, the modulation scheme determination unit determining a uniformchannel coding rate over the plural divided sequences.
 19. Thetransmitter as claimed in claim 12, the modulation scheme determinationunit determining a channel coding rate applied to the data sequence tobe divided.
 20. The transmitter as claimed in claim 12, the divisionunit dividing the data sequence depending on a number of pluraltransmission antennas.
 21. The transmitter as claimed in claim 12, thedivision unit dividing the data sequence to be transmitted into agreater number of sequences than a number of transmission antennas. 22.The transmitter as claimed in claim 4, the modulation schemedetermination unit determining transmission power for the data channelfor each of the frequency blocks.
 23. The transmitter as claimed inclaim 22, further comprising: a storage unit storing a predefinedcorrespondence between modulation schemes for the data channel andtransmission power levels.
 24. The transmitter as claimed in claim 22,wherein the control channel includes information indicative of thetransmission power of the data channel.
 25. The transmitter as claimedin claim 22, wherein the control channel indicating that thetransmission power for at least one frequency block is equal to zero istransmitted to the selected communicating opponents at a transmissiontiming for the control channel different from a control channelindicative of assignment of frequency blocks for the communicatingopponents.
 26. A method of transmitting data to a communicating opponentwith a better channel condition with use of one or more frequency blocksincluding one or more carrier frequencies; the method comprising thesteps of: evaluating the channel condition for each of the frequencyblocks for each of plural communicating opponents; selecting one or moreof the communicating opponents from the plural communicating opponents;determining at least a modulation scheme depending on the evaluatedchannel condition; generating a control channel indicative of thedetermined modulation scheme and one or more of the frequency blocksavailable for the selected communicating opponents to receive data; andproviding the selected communicating opponents with the control channeland a data channel modulated in accordance with the modulation scheme.27. The transmitter as claimed in claim 2, wherein the modulation schemeis determined for each of the frequency blocks.
 28. The transmitter asclaimed in claim 3, wherein the modulation scheme is determined for eachof the frequency blocks.
 29. The transmitter as claimed in claim 2,wherein the modulation scheme is determined uniformly over the pluralfrequency blocks.
 30. The transmitter as claimed in claim 3, wherein themodulation scheme is determined uniformly over the plural frequencyblocks.
 31. The transmitter as claimed in claim 2, wherein themodulation scheme is determined uniformly over plural subcarriersdistributed over a frequency axis.
 32. The transmitter as claimed inclaim 3, wherein the modulation scheme is determined uniformly overplural subcarriers distributed over a frequency axis.
 33. Thetransmitter as claimed in claim 2, further comprising: a division unitdividing a data sequence to be transmitted into plural sequences, themodulation scheme determination unit determining at least a modulationscheme for each of the plural divided sequences.
 34. The transmitter asclaimed in claim 3, further comprising: a division unit dividing a datasequence to be transmitted into plural sequences, the modulation schemedetermination unit determining at least a modulation scheme for each ofthe plural divided sequences.